Loss of a membrane phase under soft confinement conditions imposed by a porous silica colloids network

Abstract

Poly(ethylene glycol) mono-alkyl ether (CnEm) nonionic surfactants can form various liquid crystalline phases in water that are not altered by a change of pH nor by the presence inorganic materials. Their nonionic membrane phases were thus used as model system to mimic biological cell membranes and their behavior in the presence of inorganic colloids. In this study, a membrane phase formed by the triethylene glycol monodecyl ether (C10E3) nonionic surfactant was used as a model system to study the impact of topological constraints, and other confinement effects imposed / induced by aerosil gels. Smoked silica aerosil nanoparticles formed porous gels when aerosils interacted by siloxane bonds, in which both the pore volume and surface disorder were modulated by the concentration of nanoparticles with diameters of 7, 16, 20 & 40 nm. With the use of small angle X-ray scattering (SAXS) and polarized optical microscopy (POM) techniques as probes, the nonionic membranes could be stabilized at high temperatures, up to 8 °C higher than with bulk systems. These collapsed at high aerosil concentrations where, however drastic effects of confinement (finite size, interaction to the surface) altered the rigidity of the membranes. These effects led to a slowing down of the dynamics and a change in the elastic properties of the membranes that were not able to adapt within the aerosil gels, leading to their collapse into micellar phases. Since aerosils gels can be aligned by weak stimuli, one of a research prospects may concern the understanding of the confinement of nonionic membrane phases formed by the C10E3 as well as other CnEm surfactants in these anisotropic soft confinement matrixes.